700 Fossils from China's Jiangchuan Biota Push Complex Animal Origins Back Before the Cambrian Explosion
A trove of late Ediacaran fossils in Yunnan province reveals bilaterians, deuterostomes, and comb jellies existed at least four million years before the Cambrian explosion, reshaping the timeline of animal evolution.
Overview
An international team of paleontologists has described more than 700 fossils from a newly identified site in southwest China that demonstrate complex animals were already diversifying during the late Ediacaran period, at least four million years before the Cambrian explosion traditionally considered the dawn of animal life. The findings, published in the journal Science on April 3, 2026, introduce the Jiangchuan biota as a critical window into the transition from simple Ediacaran organisms to the complex body plans that dominate the modern animal kingdom.
What We Know
The fossils were recovered from a site in Yunnan province near the UNESCO-listed Chengjiang world natural heritage site, according to PBS News. Chinese and British researchers conducted multiple excavation campaigns between 2022 and 2025, collecting specimens that date to between 554 and 539 million years ago.
Unlike most Ediacaran fossil sites, where organisms survive only as impressions in sandstone, the Jiangchuan specimens are preserved as thin carbon-rich films, according to the University of Oxford. This type of preservation, more typical of famous Cambrian sites such as Canada’s Burgess Shale, reveals anatomical details rarely seen in fossils of this age, including feeding structures, digestive systems, and organs used for movement.
Among the most significant finds are what appear to be the earliest known deuterostomes, the animal group that includes all vertebrates as well as starfish and sea urchins, as reported by ScienceDaily. Previously, the oldest confirmed deuterostome fossils dated to the Cambrian period. The assemblage also includes ambulacrarian fossils with U-shaped bodies and tentacles, worm-like bilaterians with complex feeding strategies, and early comb jellies.
The study was led by Dr. Gaorong Li of Yunnan University, now at the Oxford University Museum of Natural History, alongside Dr. Frankie Dunn, Associate Professor Luke Parry, and Associate Professor Ross Anderson of Oxford, as well as Professor Peiyun Cong and Associate Professor Fan Wei of Yunnan University and Professor Feng Tang of the Chinese Academy of Geological Science in Beijing, according to ScienceDaily.
What We Don’t Know
The precise evolutionary relationships between the Jiangchuan organisms and their Cambrian descendants remain to be worked out. Some specimens display unusual combinations of features that do not match any known living or extinct species, as noted by the University of Oxford, raising questions about whether they represent stem groups, evolutionary dead ends, or ancestors of lineages that survived into the Phanerozoic.
The site’s full extent has not yet been mapped. Researchers have indicated that further excavation could yield additional species and help clarify how quickly animal body plans diversified during the final millions of years of the Ediacaran.
It also remains unclear what environmental conditions allowed such exceptional preservation at this particular site, and whether similar assemblages might be found at other late Ediacaran localities worldwide.
Significance
The discovery directly addresses a long-standing tension in evolutionary biology known as the “rocks versus clocks” debate. Molecular clock studies, which estimate divergence times from DNA mutation rates, have long suggested that major animal groups originated well before the Cambrian. The fossil record, however, has offered limited physical evidence to support those predictions. The Jiangchuan biota provides that missing physical evidence, according to PBS News, demonstrating that bilateral symmetry, deuterostome body plans, and three-dimensional movement were all present before the Cambrian boundary.
The paper, titled “The dawn of the Phanerozoic: a transitional fauna from the late Ediacaran of Southwest China,” appears in Science volume 392, issue 6793.